Surprise Fire Threat? Clogged Chimneys It's a winter household hazard that can be tough for the eye to see, and if you miss it, it can be costly or even deadly. Now's the time to prevent it. Clogged chimneys can cause fires this time of year. A family in Hudson, Wis., had one just last night, as build-up in the chimney was the impetus. Luckily, as smoke poured into the room, they got out.